Brake



Feb. 1, 1944. GATES 2,340,464

BRAKE Filed March 20, 1941 2 Sheets- Shee't 1 ATTORNEY Feb. 1, 1944.GATES 2,340,464

. BRAKE Filed March 20, 1941 2 Sheets-Sheet 2 I um Patented Feb. 1, 1944BRAKE Geoffrey Robert Greenbergh Gates, Leamington Spa, England,assignor to Automotive Products Company Limited, Leamington Spa, EnglandApplication March 20, 1941, Serial No. 384,409 In Great Britain April 5,1940 2 Claims.

This invention relates to internal shoe brakes of the type comprisingtwo substantially rigid arcuate shoes pivotally mounted on a commonanchorage abutment oron adjacent abutments, and a spreading devicebetween the un-anchored ends of the shoes. In brakes of this type, oneof the shoes, when applied to the drum, tends to be urged more firmlyinto engagement with the drum by the rotation of the latter, and iscommonly referred to as the leading shoe, whilst the other shoe,commonly referred'to as the trailing shoe, tends to be urged away fromthedrum by the rotation of the latter, the leading shoe being that shoealong which a point on the drum surface travels from the spreadingdevice to the anchored end. The brake, according to the presentinvention, is intended for use on a motor road vehicle which travelsalmost exclusively in one direction, being only occasionally driven inthe reverse direction, and the brake shoes which are referred to hereinas the leading shoe and trailing shoe respectively are those which actin those capacities when the vehicle is travelling in its normaldirection.

The principal object of the invention is to provide an improved means ofadjusting the shoes of a brake of the type referred to, to compensatefor wear of the friction surfaces.

According to the invention, the spreading device, which is mounted forlongitudinal sliding movement between the shoe ends, forms a rigidspacer for said shoe ends when the brake is not applied, and anadjusting means is provided for moving the trailing shoe outwardly intocontact with the drum, the said shoe being subsequently spaced from thedrum to a small extent by the distortion of the drum when the brakes areapplied with the vehicle in motion, thus moving the spreading devicetowards the leading shoe to centralize the shoes in the drum.

prise a plunger and cylinder unit capable of angular movement in theplane of the brake shoes, and pivotally engaged with the leading shoe.

The invention is hereinafter described with reference to theaccompanying drawings, in which:

Figure 1 is a side elevation of a brake according to the invention;

Figure 2 is a view corresponding to Figure 1, but on a larger scale, andwith certain parts in section; I

Figure 3 is a section on the line 3--3 of Figure 2; and

- Figures 4 and 5 are diagrams showing how the brake shoes arecentralized by the drum distortion.

Referring to Figures 1 to 3, a brake, the drum of which rotatesnormallyin a clockwise direction, comprises a pair of shoes ill, I Imounted on separate anchor pins l2, IS on a back plate l4 and a liquidpressure wheel cylinder l5 mounted on the back plate between theun-anchored ends of the shoes. The shoe Ill is normally the trailingshoe, and the shoe II the leading shoe. The wheel cylinder 15 is formedwith a spigot [6 projecting in a direction perpendicular to its bore H,which spigot passes through a hole H3 in the back plate and is retainedin position by a spring ring 20 between which and the back plate isawasher 2| of friction material. The hole I8 through which the spigotpasses is elongated in the direction of the axis of the wheel cylinderl5, so that the latter is capable of both rotary and translationalmovement, such movement being resisted to a slight degree by thefriction between the washer 2| and the back plate. In the cylinder 15are mounted two opposed pistons 22 and According to another aspect ofthe invention,

the spreading device, which is mounted for longitudinal sliding movementbetween the shoe ends, forms a rigid spacer for the said shoe ends whenthe brake is not applied, and an adjusting means is provided which actson the leading shoe, and, through the spreading device, on the trailingshoe, to move both shoes outwardly into contact with the drum, theleading shoe being then spaced from the drum by reverse movement of theadjuster, and the shoes being centred by the distortion of the drum whenthe brakes are applied with the vehicle moving in a forward direction.

The adjusting device may be disposed between the spreading device andone of the shoes, and the spreading device may be a fluid pressure wheelcylinder. The Wheel cylinder may comprise an open ended cylinder inwhich operate opposed plungers whose movement into the cylinder islimited. The spreading device may com- 23 provided with suitablefluid-tight packings '24. The piston 22 which acts on the trailing shoeI0, is solid, and is formed at its outer end with'an, annular flange 25adapted to engage with the end of the cylinder l5 and limit the movementof the piston into' the cylinder. The outer end surface 26 of the pistonis fiat, and is engaged by the arcuate edge of a projection 21 formed onthe web of the trailing shoe Ill. The second piston 23 is deeplyrecessed from its outer end at 28 to receive the threaded end of anadjusting plunger 30 threaded into the base of a cap 3| fitting slidablyover the end of the wheel cylinder IS, the base of the cap 3| beingadapted to engage both the end of the cylinder, l5 and the end of thepiston 23. The outer end of the adjusting plunger 3!! is enlarged toform a head 32, and is slotted at 33 to embrace a projection 34 on theleading shoe web similar to the projection 21 on the trailing shoe, thebase of the slot 33- being of concave arcuate form to correspond to theshape of the projection 34. The plunger 30 is thus restrained againstrotation by the web of the shoe.- The edge of the cap 3| is turnedoutwardly, and formed with a series of notches 35 to co-operatewithaspring finger36 mounted on the cylinder, ithecap being rotatable onthe cylinder by engaging a tool in the notches 35, but

being held against free rotation by the spring two pistons 22 and 23,the piston 22 associated with the trailing shoe l acting directly onthat shoe, whilst the piston 23 associated with the leading shoe appliesan outward thrust to the cap 3 "such thrust being transmitted throughthe adjusting plunger {39 to the shoe H.

The arcua'te slot 33 on the plunger 30, by its engagement withtheprojection't lon the leading shoe I'l,-causes the wheel-cylinder 1 5 tofollow the movements of the leading shoe, the centre of curvature of theprojection 34 remaining always on the longitudinal axis of the wheelcylinder [5, which axis thus tends to turn slightlyabout the mountingspigot 16 of the cylinder as the shoe It moves. The pressure is thusalways transmitted to the leading shoe along the longitudinal axis orthe cylinder, and no side loads are applied to the piston 23.

As the piston 22 is flanged at 25 to engage one end of the wheelcylinder, and the cap 3! .in which the adjusting plunger 301'is mountedengages the' other end of the wheel "cylinder, the cylinder, when "thebrakes are off, forms a rigid ispacer for the 1511085 and limits their.movement :away from the drum. The location of the shoes is thusdependent on the 'position of the wheel cylinder.

Adjustment of the shoes 'to reduce the clearance between the linings andthe drum when the former have worn .down is effected by rotating the:cap 131' cn'th'e "wheel cylinder, .to cause the adjusting plunger 3!!"threaded'thereinto to move outwardly. ESuch outward rmovement firstofiallebrings the leadingshoerl i into contact with the 'drum 38, andthen causes :the cylinder to movein the opposite direction, takingwithit the trailing :ShLOE'IJiStOIl 22, the vflange of which remains inengagement with the end of the wheel cylindenuntil the'trailing shoe Illalso engages the drum 138. The adjusting plunger is thenwithdrawnslightly by rotating the cap 3i in the reverse :direction toprovide a :slight clearance between the leadingzshoe H and the drum 38,the cylinder 15 being held in its new position by the friction betweenthe washer El and the back plate, so thatthe trailingshoe Hi remains incontact with the drum. The vehicle is then set in motion :in the forwarddirection, and pressure applied to the :pistons Hand 23 in the wheelcylinder. As the trailingshoe is alreadyiin contact with the drum,-1onlythe piston .23 is moved outwardly, and the distortion of the drum due tothe :greater pressure :of the leading shoe 'li causes the end of thetrailing shoe 10 adjacent the wheel cylinder to move inwardly, thusmov-- ing the wheel cylinder 15 slightly in the direction-oi therleadingishoe to distribute thecleararise :between the two shoes. It hasbeen found that, with :a brake comprising a leading and a trailing shoe:the drum tends to distort during braheapplication to a somewhatelliptical form, with its major axis through the drum centre and theTapproximate :centres of the shoes, and its minor axis :spiaced slightlyfrom the true drum centre towards the leading shoe. This distortion isshown by the .lfull-line .position of the drum in Eigure 5, which .is ofcourse much exaggerated, and by comparison with Figure 4 it can .be seenthat the trailing shoe I0 is in substantially the same position whenengaged with the distorted drum as when free with the drum concentricwiththe back plate.

tained at the trailing shoe tip is of course equal The clearance obtotheiiisp'lacementof the drum due to distortion at this point, and propercentralization of the shoes "-is obt'ain'ed by slacking back theadjuster, after both shoes have touched the drum, until the leading shoetip clearance is twice that given at the trailing shoe tip by the drumdistortion. The trailing .shoe, having :been in engagement with the drumwhilst the latter was undistorted, will have tits end nearer to :thewheel cylinder moved inwardly when, :owing to the zapplication of the-b1takes,1the drum is distorted, :thus 'producing the sslig'ht :movementof the wheel cylinder required to centralize the shoes.

A thin metal cap ;39 extending :over the :wall of the -;cylinder 15 isattached to the piston 22 operating-the :trailing shoe,to' prevent theentry of dust and water into the cylinder.

WhatI claim .is:

1. In a brake :having a trailing shoe :and -'a leading .shoe, :a"spreading :device which is frictionally mounted for longitudinalsliding .movement and for angular 'movement :between the shoe endsandwhich Lforms a rigid spacer for said shoe ends when the brake is not:applied, said spreading device comprising an :open-ended fluid pressurewheel cylinderhaving opposed p-lungersv operating therein and havingmeans for limiting the inward movement of the plungers, andadjustingmeansat one end ;of the spreading device and pivotally engagedby the end .01" the leading shoe and operable for moving the trailingshoe outwardly into contact with .the drum, the said shoe beingsubsequently spaced :from the drum to a small-extent by the distortion,of the :drum when the brakes are applied with the vehicle in motion,thus moving thelspreading device toward the leading .shoe to centralizethe shoes in the drum, said adjusting means comprising a screwed plungerpivotally engaged by the end of the leading shoe .and:adjustablerelatively to one of the wheel cylinder plungers and threadedinto a cap engaging the end of the wheel cylinder, said cap beingadapted to beengaged on its inner face by the 'wheel cylinderplunger.

2. Ina brake having atrailingshoeand a leading shoe, a spreading devicewhich comprises a plunger and cylinder unit frictionally movably mountedand capable of angular movement in the plane of the brake shoes andwhich is mounted for longitudinal sliding movement between the shoeends, said spreading device forming a rigid spacer for said shoe endswhen 'the brake is not applied and pivotally engaging .the leading shoe,and an adjusting means associated with the sliding device which :ispivotally engaged by the end of the leading shoe and which acts on theleading shoe and through the spreading device on the trailing shoe tomove .both shoes outwardlyzinto contact with the drum, the leading shoebeing then spaced from the drum by reverse movement of the adjuster, andthe shoes being centered by the distortion ofthedrumwhen the brakes .areapplied with the vehicle moving ina forward direction.

eEoFE-REY ROBERT GREENE; ERGI-I GATES.

